1. Field of the Invention
The present invention relates to a segmented gas turbine stationary blade unit in which two stationary blades are assembled in one shroud unit so as to reduce the influence of thermal stress on the blades or shroud and to avoid occurrence of cracks.
2. Description of the Prior Art
In gas turbine stationary blades, air leaks from an inner side through a gap between mutually adjacent inner shrouds is discharged into combustion gas passage, which results in an increased power burden on the compressor. Recently, in order to lessen the gap which causes the leakage, trials are being performed in order to make the stationary blades in a segmented form. In this case, plural stationary blades are fixed in one unit by shrouds, hence there occurs a large restraining force between the blades and this causes local stress concentrations due to thermal stress, and thus cracks occur frequently.
FIGS. 10(a) and (b) are perspective views of a prior are segmented stationary blade unit showing a state of occurrence of cracks.
In the figures, numeral 1a, 1b designate stationary blades, respectively. Numeral 22 designates an outer shroud and numeral 23 designates an inner shroud. The two stationary blades 1a, 1b are fixed in a shroud unit comprising the outer shroud 22 and the inner shroud 23 so as to form a segment.
When the stationary blades 1a, 1b are constructed as a single unit, the stationary blades 1a, 1b and the outer and inner shrouds 22, 23 are mutually restrained so that unreasonable or large forces occur due to thermal stress, and thus cracks are liable to occur in an inner side portion P3 of the stationary blade 1a and in a portion S1 of the inner shroud 23, as shown in FIG. 10(a). Cracks are also likely to develop in both end portions P1, P2 of the stationary blade 1a and in a portion S2 of the inner shroud 23, as shown in FIG. 10(b).
In the gas turbine stationary blades, as mentioned above, in order to reduce leakage of the seal air, trials are being performed a to make the stationary blades segmented so as to lessen the gap between mutually adjacent inner shrouds. On the other hand, when the stationary blades are segmented, the restraining force becomes a larger, thus stress local concentrations occur due to thermal stress, and thus cracks occur frequently.